The drilling of radial horizontal wells is an effective method for improving the oil and gas production. Due to the existence of radial holes, the stress filed surrounding the well is redistributed. Under such circumstance, the initiation and propagation of hydraulic fractures are different with those in traditional fracturing. Therefore, it is necessary to study the influences of radial horizontal wells on the initiation and propagation of the fracturing fractures. The laboratory experiment was conducted to simulate the hydraulic fracturing on the physical model with radial holes. The experimental results showed that, compared with the borehole without radial holes, the sample with radial holes in the direction of maximum horizontal stress was fractured with significantly lower pressure. As the angle between direction of the horizontal hole and the direction of maximum horizontal stress increased, the fracture pressure grew. While when the radial hole was drilled towards the direction of the minimum horizontal stress, the fracture pressure increased to that needed in the borehole without radial holes. When the angle between the radial hole and the maximum horizontal stress increase, the pressure required to propagate the fractures grew apparently, and the fracture become complex. Meanwhile, the deeper the radial hole drilled, the less the pressure was needed for fracturing.

1. Introduction

As ultra-low permeability reservoirs are characterized by large burial depth and poor physical properties, resulting in low productivities, they have to be fractured in the reservoirs in practical engineering(Qi et al. 2012; Dingwei et al. 2011; Adams and Rowe, 2013). Radial horizontal drilling technique is an effective method to improve oilfield development(Li and Shen, 2005; Marbun et al. 2011). However, when merely using several radial drillings techniques in the low permeability reservoirs, insufficient well-drainage areas and small increase of oil and gas productions are likely to occur. Therefore, a combination of a radial horizontal drilling technique and hydraulic fracturing technology can largely improve the permeabilities of formations and increase well-drainage areas(Fu et al. 2016). The combination presents broad application prospects in the development of low permeability reservoirs.

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